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| Titel |
Quantifying the impact of groundwater depth on evapotranspiration in a semi-arid grassland region |
| VerfasserIn |
M. E. Soylu, E. Istanbulluoglu, J. D. Lenters, T. Wang |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 15, no. 3 ; Nr. 15, no. 3 (2011-03-07), S.787-806 |
| Datensatznummer |
250012681
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| Publikation (Nr.) |
 copernicus.org/hess-15-787-2011.pdf |
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| Zusammenfassung |
| Interactions between shallow groundwater and land surface processes play an
important role in the ecohydrology of riparian zones. Some recent land
surface models (LSMs) incorporate groundwater-land surface interactions
using parameterizations at varying levels of detail. In this paper, we
examine the sensitivity of land surface evapotranspiration (ET) to water
table depth, soil texture, and two commonly used soil hydraulic parameter
datasets using four models with varying levels of complexity. The selected
models are Hydrus-1D, which solves the pressure-based Richards equation, the
Integrated Biosphere Simulator (IBIS), which simulates interactions among
multiple soil layers using a (water-content) variant of the Richards
equation, and two forms of a steady-state capillary flux model coupled with
a single-bucket soil moisture model. These models are first evaluated using
field observations of climate, soil moisture, and groundwater levels at a
semi-arid site in south-central Nebraska, USA. All four models are found to
compare reasonably well with observations, particularly when the effects of
groundwater are included. We then examine the sensitivity of modelled ET to
water table depth for various model formulations, node spacings, and soil
textures (using soil hydraulic parameter values from two different sources,
namely Rawls and Clapp-Hornberger). The results indicate a strong influence
of soil texture and water table depth on groundwater contributions to ET.
Furthermore, differences in texture-specific, class-averaged soil parameters
obtained from the two literature sources lead to large differences in the
simulated depth and thickness of the "critical zone" (i.e., the zone
within which variations in water table depth strongly impact surface ET).
Depending on the depth-to-groundwater, this can also lead to large
discrepancies in simulated ET (in some cases by more than a factor of two).
When the Clapp-Hornberger soil parameter dataset is used, the critical zone
becomes significantly deeper, and surface ET rates become much higher,
resulting in a stronger influence of deep groundwater on the land surface
energy and water balance. In general, we find that the simulated sensitivity
of ET to the choice of soil hydraulic parameter dataset is greater than the
sensitivity to soil texture defined within each dataset, or even to the
choice of model formulation. Thus, our findings underscore the need for
future modelling and field-based studies to improve the predictability of
groundwater-land surface interactions in numerical models, particularly as
it relates to the parameterization of soil hydraulic properties. |
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